Re: gcc-4 troubleshooting

[Matthew Heine <mheine () sigovs com>]

+    for(; ifr && *((u8 *)ifr) && ((u8 *)ifr) < ((u8 *)ifr) + ifc.ifc_len; 
I think this last changed line should be 


+    for(; ifr && *((u8 *)ifr) && ((u8 *)ifr) < ((u8 *)buf) + ifc.ifc_len; 

instead. 


Duilio Protti wrote:

> Fyodor wrote:
>
> > While this works for now, a better approach might be to find all the
> > lines that apparently violate C99 alias rules and fix them.  Here is
> > an example that SoC student Paul Tarjan found (from tcpip.cc):
> >
> > buf = (u8 *) safe_zalloc(bufsz);
> > [...]
> > ifr = (struct ifreq *) buf;
> > [...]
> >   for(; ifr && *((u8 *)ifr) && ((u8 *)ifr) < buf + ifc.ifc_len;
> >        ((*(char **)&ifr) += len ))
> >
> > I don't know if it is technically legal or not, but gcc doesn't seem
> > to like it with -O2.  It is pretty gross anyway, and deserves to be
> > changed for that reason if no other.
> >
> >  
>
> An example similar to the code above can be found on a post by Marcus 
> Brinkmann here:
>
> http://lists.gnu.org/archive/html/l4-hurd/2005-01/msg00027.html
>
> According to Marcus, the following code is good (for aliasing rules):
>
>  struct a;
>
> struct a_d { struct a a_m; int etc; };
>
> struct a_d a_i;
> struct a *ap = &a_i.a_m;
>
> But this other one doesn't respect well the mentioned rules:
>
> struct a *ap = malloc (sizeof (struct a_d));
>
> struct a_d *adp = (struct adp *) ap;
>
>
> With this in mind, the tcpip.cc fragment above can be changed in the 
> form described on the attached patch.
>
>
> Bye,
> Duilio.
>
> ------------------------------------------------------------------------
>
> --- tcpip.cc.orig      2005-08-29 15:40:32.000000000 -0300
> +++ tcpip.cc   2005-08-29 16:38:22.000000000 -0300
> @@ -2159,10 +2159,10 @@
>   struct ifconf ifc;
>   struct ifreq *ifr;
>   struct ifreq tmpifr;
> +  struct ifreq *buf;
> #endif
>   int len, rc;
>   char *p;
> -  u8 *buf;
>   int bufsz;
>   struct sockaddr_in *sin;
>   u16 ifflags;
> @@ -2194,13 +2194,13 @@
>     sd = socket(AF_INET, SOCK_DGRAM, 0);
>     if (sd < 0) pfatal("socket in getinterfaces");
>     bufsz = 20480;
> -    buf = (u8 *) safe_zalloc(bufsz);
> +    buf = (struct ifreq *) safe_zalloc(bufsz);
>     ifc.ifc_len = bufsz;
>     ifc.ifc_buf = (char *) buf;
>     if (ioctl(sd, SIOCGIFCONF, &ifc) < 0) {
>       fatal("Failed to determine your configured interfaces!\n");
>     }
> -    ifr = (struct ifreq *) buf;
> +    ifr = buf;
>     if (ifc.ifc_len == 0) 
>       fatal("getinterfaces: SIOCGIFCONF claims you have no network interfaces!\n");
> #if HAVE_SOCKADDR_SA_LEN
> @@ -2219,7 +2219,7 @@
>     printf("Size of struct ifreq: %d\n", sizeof(struct ifreq));
> #endif
>
> -    for(; ifr && *((u8 *)ifr) && ((u8 *)ifr) < buf + ifc.ifc_len; 
> +    for(; ifr && *((u8 *)ifr) && ((u8 *)ifr) < ((u8 *)ifr) + ifc.ifc_len; 
>       ((*(char **)&ifr) += len )) {
> #if TCPIP_DEBUGGING
>       printf("ifr_name size = %d\n", sizeof(ifr->ifr_name));
>  
>
> ------------------------------------------------------------------------
>
>
>
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>  


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